Aiming at the Moon: the burn that throws you there
8 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
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The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
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Orbital speed: why lower orbits go faster
9 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
Circularising: the burn that makes it stay up
8 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
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All episodes
Aiming at the Moon: the burn that throws you there
8 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
Orbital speed: why lower orbits go faster
9 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
Circularising: the burn that makes it stay up
8 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
The gravity turn: why rockets lean over
9 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
Why prograde raises the far side
8 min
From Orbit 101: The beginner’s course: why an orbit is falling and missing the ground, and what each control on the map really does.
Apoapsis and periapsis: the high point and the low point
8 min
This is Orbital Radio. Out here, you’re never alone. Here’s a riddle. Your ship is in orbit, engines off. Nothing’s pushing it. Nothing’s touching it. Up above the air, there’s nothing to slow it down. And yet, unless your orbit is a perfect circle, the speed on the navball won’t sit still. For half of every lap it climbs. For the other half it sinks. So who’s working the throttle? Nobody. Your ship is rolling around a bowl. And every bowl has a top and a bottom. Today on Orbital Radio, the high point and the low point. By the end of this show, you’ll know why nearly every orbit has one of each, and what Orbital Frontier calls them. You’ll know why your ship is fastest at one and slowest at the other. And you’ll know why it spends most of its time up high. On another show, we fired Isaac Newton’s cannon from a mountain so tall that its top pokes out above the air. Fire the ball sideways at just the right speed, and it falls all the way around the world at the same height. A perfect circle. But what if you get the speed a little wrong? Fire it a little faster, and the ball still comes all the way round. But on the far side of the world, it swings out higher. Fire it a little slower, and the far side dips lower. Either way, the ball comes back to the mountain top, again and again. The path has simply been stretched. That stretched loop is called an ellipse. Tilt a glass of water and look down at the water’s surface. That oval is an ellipse. And here’s the clever part. The world doesn’t sit in the middle of the oval. It sits off towards one end. Picture a long running track, with the Earth standing near one end of the field instead of in the middle. One end of the track passes close to the Earth. The other end swings far away. That’s the shape of nearly every orbit there is. One near end, one far end. People worked this out long before anyone flew. In sixteen oh nine, the astronomer Johannes Kepler worked it out from years of careful measurements of Mars. The p...
Falling around the world: what an orbit is
7 min
Let’s start with a question that sounds like a trick. Your ship is in orbit around the Earth. A hundred kilometres up, engines off, everything quiet. So what’s holding it up there? Nothing. Nothing at all is holding it up. Your ship is falling. It started falling the moment the engine went quiet, and it will keep falling as long as you leave it there. That isn’t something wrong with your orbit. That is your orbit. Today on Orbital Radio, we’re falling around the world. By the end of this show, you’ll know what an orbit really is, and why your ship never comes down on its own. You’ll know the two marks on the map that say whether you’ve got one. And next time you fly in Orbital Frontier, you’ll see it for yourself. First things first. Gravity never lets go. There’s no height where it switches off. A hundred kilometres above the Earth in Orbital Frontier, it’s still pulling about three quarters as hard as it does on the launch pad. Space isn’t a place without gravity. It’s a place without air. You can watch gravity at work. Find the navball, the round dial that shows which way your ship is pointing. Just to its left is a figure marked with the letters V and S. That’s your vertical speed, how fast you’re going up or down. When the engine stops on your way up, that number starts shrinking, every single second, as gravity takes its bite. It doesn’t care that you’re in space. It just keeps pulling. So if gravity never stops, why doesn’t your ship come straight back down? More than three hundred years ago, Isaac Newton answered that with a mountain and a cannon. He wrote it down in sixteen eighty-seven, and it still works today. Picture a mountain so tall that its top pokes out above the air. On the summit sits a cannon, pointing sideways. Fire it with a little powder, and the ball arcs out and drops near the foot of the mountain. Use more powder, and it lands further away. Use a lot more, and it lands a long way off, because while it falls, it’s also racing sideway...
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